1. Field of the Invention
The present invention relates to an injection molding machine, and more particularly to an aligning device for aligning an axis of an injection nozzle with that of a sprue of a mold.
2. Description of Related Art
In an injection molding machine, a mold is closed by bringing a movable mold half attached to a movable platen into contact with a stationary mold half attached to a stationary platen, and molten resin in an injection cylinder is injected into the mold from an injection nozzle. It is therefore necessary that the axis of the sprue of the mold and the axis of the injection nozzle should be in alignment with each other.
Conventionally, as shown in FIG. 7, a peephole 20 extending obliquely with respect to the axis of the injection nozzle is formed through the stationary platen 2 in the vicinity of a locating hole so that the contact of the distal end of the injection nozzle with a sprue bushing of the mold can be viewed through the peephole. The positional relationship between the injection nozzle and the sprue bushing is observed through the peephole 20 to accurately bring the injection nozzle into alignment (see JP 05-329899A).
However, in the case of a mold whose sprue bushing is located inward of the mounting surface at which the mold is attached to the stationary platen (i.e., located closer to the interior of the mold), it is often impossible to observe the positional relationship between the injection nozzle and the sprue bushing.
Also, in a small-sized injection molding machine, a small-sized mold is used, and in order to obtain sufficient rigidity of the stationary platen and of the mold, a small locating hole is formed through the stationary platen. It is therefore difficult to form a peephole, as seen from FIG. 8, and even if a peephole is formed, the position of contact between the distal end of the injection nozzle 5 and the sprue bushing of the mold cannot be observed.
Accordingly, when aligning the injection nozzle 5, the stationary mold half is detached from the stationary platen 2, the injection nozzle 5 is inserted into the locating hole of the stationary platen, and the position of the injection nozzle 5 is adjusted from the side of the mold mounting surface of the stationary platen such that the distal end of the injection nozzle 5 inserted into the locating hole is located at the center of the locating hole.
There has also been known a method using an axis aligning jig for aligning the distal end of the nozzle with the sprue of the mold (see JP 03-124413A). This method uses an axis aligning jig which includes a protrusion to be fitted into the nozzle insertion hole of the stationary platen, a center shaft tiltable relative to an axial hole formed in the center of the protrusion, and a sensor for detecting the tilt of the center shaft. The alignment of the injection nozzle with the sprue of the mold is carried out in the manner described below. The jig is attached to the injection unit side of the stationary platen, and with the mold pulled up with a crane or the like, the mold is temporarily fixed to the stationary platen. Then, the injection unit is advanced to cause the distal end of the nozzle to fit in a concave surface of the center shaft of the jig, and the value detected and indicated by the sensor is read. Subsequently, the mold is closed while being pulled up with the crane etc., and with the center shaft of the jig fitted into the sprue of the mold, the position of the stationary mold half is adjusted using a hammer or the like so that the value detected by the sensor may become equal to the previously obtained reading of the sensor.
Meanwhile, when the injection molding machine is operated to perform injection molding, the mold and an injection cylinder are heated to high temperature. Because of rise in temperature, the mold and the injection cylinder thermally expand. Consequently, there arises a difference between the vertical position where the mold should be located when the stationary mold half is detached from the stationary platen and the vertical position where the stationary mold half is located when attached to the stationary platen and heated to high temperature. Thus, even in the case where the injection nozzle is aligned while the stationary mold half is detached from the stationary platen, a small deviation occurs between the position of the injection nozzle and the position of the sprue of the mold.
It is therefore desirable that the injection nozzle should be aligned while the mold and the injection cylinder are heated to high temperature. The aligning method using the jig, disclosed in the above patent document, is applied to the alignment carried out before the mold and the injection cylinder are heated to high temperature. Also, the jig used includes a sensor etc. Thus, the jig is complicated in structure and is expensive, and also the attachment/detachment thereof is not easy.